Why Are Peonies White?

Genetics

• Genes in plants, like those in animals, determine the appearance of plants. The petals of flowers are simply adapted leaves where the production of chlorophyll has been blocked and other genes control color. Some genes produce pigments called flavones, and some produce anthocyanin pigments. Others control mixtures and color patterns or inhibit certain colors (such as the green of chlorophyll). The first white peonies carried genetic patterns that resulted in white flowers and new colors are introduced by cross-breeding plants with differing genetic structures.

Environment

• Weather, soil type and pH can encourage plants to adapt the way they grow. Altitude and latitude control the way a plant uses oxygen, its adaptation to the intensity of sunlight and length of growing seasons. Color may adapt slightly as climates and locations change. White was one aspect of the peony's adaptation to its native environment in western China.

Pollinators

• Angiosperms, plants that flower and produce seed as the result of sexual reproduction, require help moving the pollen from anthers to the stigma, the opening at the top of the long tube leading to the plant's ovary where seeds are formed. In addition to accidental pollination by wind or animals that brush by, flowers adapt by developing color and scent to attract insects or birds. To complicate matters, they must present these colors and scents must appear at a time that pollinators are present in the environment to respond in enough numbers to assure successful pollination. The white peony attracts insects such as bees that respond to the bright white. The flowers also stay open at night, attracting moths and bats.

Perception

• Pigments combine to form hues but human -- and potential insect pollinators -- perceive colors by the light reflected by the petals of a flower. Examine a white peony petal closely in bright sunlight and you will notice jewel-like glints of red, green and blue (or magenta, yellow and cyan) on its surface. The white light reflected from the peony's petals is actually results from light striking pigments from all of the color genes rather than just the genes whose reflections that cause the perception of red, yellow, blue or combination of colors. Every species perceives reflected light a bit differently; although humans might use this perception of white to design a lovely garden, natural selection produced white peonies with pigments that reflected light in a way that hungry pollinators could perceive easily.